1. Field of the Invention
The present invention relates to a polypropylene composite composition, and more specifically to a polypropylene composite composition using glass bubbles as fillers for weight reduction.
2. Description of the Related Art
In recent years, the automotive industry has succeeded in achieving convenience and environmental protection through extensive and intensive research and development. In this connection, main issues raised in the automotive component industry are concentrated on weight reduction, modulation and electronization. Automobiles, which have long been recognized as simple transportation means, are becoming living necessaries that provide various functions, such as safety, convenience, silence and sensibility, to customers. As the production and sales of hybrid automobiles are encouraged in terms of fuel efficiency, air pollution problems and oil prices, there is a rapidly increasing demand for lightweight and high-performance automobiles. Particularly, developments of high-performance plastics using glass fibers and carbon fibers have led to a reduction in the weight of car body components, such as trunks and hoods. On the other hand, governmental regulations in many countries, particularly European countries, have restricted the contents of environmentally harmful substances, particularly heavy metals, including cadmium (Cd), lead (Pb), mercury (Hg) and hexavalent chromium (Cr6+), discharged from automobiles and have enforced recycling of the substances. As a result, the weight of plastics used in each car has been steadily increasing.
Under such circumstances, continuous research has been conducted on the weight reduction through the integration and unification of materials, and replacement with olefin plastics of low specific gravity by auto makers, mainly Toyota and Nissan Motors.
On the other hand, instrument panels, which are representative automotive interior components, are divided into two types, i.e. foam type and integral hard type. The hard type instrument panels are produced by injection molding a PPF material, which is produced by compounding PP, rubbers and talc, followed by painting. Meanwhile, the foam type instrument panels are produced by injection molding a core as a structural material with a blend of PC and ABS as an engineering plastic. In recent years, the use of foamable core products, to which PPF materials are applied, has increased in view of integration of materials and reduction of cost and weight. However, the problems of such foamable core products are negligible weight reduction effects and increased number of defects due to low resin fluidity and poor dimensional stability during foaming. Thus, there is a growing interest in fillers capable of replacing talc. Glass bubbles produced by 3M have drawn considerable attention as fillers for weight reduction.
Glass bubbles are three-dimensional hollow microspheres and are fillers composed essentially of soda-lime borosilicate. Glass bubbles have a particle size of 14 to 135 μm and a specific gravity of 0.125 to 0.6. For purposes of comparison with glass bubbles, the kind and specific gravity of several fillers used in plastics are presented in Table 1 below.
TABLE 1FillerSpecific gravityFillerSpecific gravityCaCO32.70Glass Fiber2.50Talc2.90TiO24.10Kaolin2.60Al2O32.50BaSO44.60Glass Beads2.50Mica2.75Glass bubble0.125-0.60
As can be seen from the data shown in Table 1, a glass bubble has a lower specific gravity than other fillers used in plastics. Based on this advantage, glass bubbles are partially used for weight reduction of components through partial replacement of high-weight fillers, such as talc and glass fibers, used in plasticizers for PVC coating, epoxy structural foams, sheet molding compounds (SMCs), bulk molding compounds (BMCs), and reaction injection moldings (RIMs). In addition to weight reduction effects due to low specific gravity, the use of glass bubbles is expected to contribute to decreased amount of resins used, good dimensional stability, less deformation after molding, and improvement of processability, moldability, heat insulation performance and water resistance. Car components that benefit from the use of glass bubbles include body side moldings (TPU), headlight housings (PC), gas tank floats (Nylon), fan shrouds (Nylon), FEM carriers (Nylon), and the like.
However, since polypropylene is incompatible with glass bubbles, the use of a combination of polypropylene and glass bubbles as a filler causes deterioration of mechanical properties of polypropylene compound materials, such as IZOD impact strength, flexural modulus and flexural strength, tensile strength, elongation and thermal deformation temperature. For these problems, composites using glass bubbles as fillers have not yet been put to practical use.
Thus, there is a strong need to develop a composite composition for weight reduction of automotive components, and particularly, a composite composition capable of improving the compatibility between polypropylene and glass bubbles.